Disk drive devices using various kinds of recording disks, such as optical disks, magneto-optical disks, flexible magnetic disks, and the like, have been known in the art. In particular, hard disk drives (HDDs) have been widely used as storage devices of computers and have been one of indispensable storage devices for current computer systems. Moreover, the HDDs have found widespread application to moving image recording/reproducing apparatuses, car navigation systems, cellular phones, and the like, due to their outstanding characteristics.
A magnetic disk used in an HDD has multiple concentric data tracks; each data track records multiple servo data having address information and multiple data sectors containing user data thereon A head element portion accesses a desired data sector in accordance with address information in the servo data to write data to and retrieve data from the data sector.
The head element portion is formed on a slider; the slider is bonded to a suspension of an actuator. The assembly of the actuator and the head slider is called a head stack assembly (HSA) and the assembly of the suspension and the head slider is called a head gimbal assembly (HGA).
Pressure caused by air viscosity between the air bearing surface (ABS) of the slider facing the magnetic disk and a spinning magnetic disk balances pressure toward the magnetic disk added by the suspension so that the head slider flies over the magnetic disk with a specific gap. The actuator pivots about a pivotal shaft to move the head slider to a target track and position it onto the track.
As the track per inch (TPI) in the magnetic disk increases, improvement in positioning accuracy of a head slider is required. However, it is getting more difficult to improve the positioning accuracy in driving an actuator by a voice coil motor (VCM). Therefore, an approach has been proposed that mounts a compact actuator (microactuator) on a tip end of the actuator to achieve a finer positioning (for example, refer to U.S. Patent Publication No. 2006/0044698 “Patent Document 1”).
The microactuator in Patent Document 1 has a piezoelectric element fixed onto the end of a substrate. The head slider is bonded to around the center of the substrate surface. As the piezoelectric element expands or contracts in an in-plane direction, beams having spring properties formed on the substrate are finely displaced in the in-plane direction to rotate the head slider. This achieves a highly accurate positioning of the head element portion to a desired position.
For highly accurate positioning control by the microactuator in a sufficient range, it is important to increase the expansion and contraction stroke of the piezoelectric element. Since the piezoelectric element expands or contracts in response to application of a voltage, increasing the voltage applied to the piezoelectric element results in increasing the stroke. However, the source voltage applied to an HDD from the external is a preset constant voltage of approximately 12 V. Mounting a booster circuit on the HDD leads to raising a supply voltage from the external to apply a higher voltage to the piezoelectric element. However, in order to achieve a simpler circuit configuration and a less expensive cost, it is preferable not to employ such an additional circuit.
Consequently, it is desired to increase the expansion and contraction stroke as much as possible within a limited voltage range by the structure of the piezoelectric element without employing an additional circuit. Various structures have been proposed for a piezoelectric element as in the following documents and others.
However, the inventors have found that a microactuator with a piezoelectric element has a problem that elastic deformation of the substrate influences the expansion and contraction stroke of the piezoelectric element (displacement amount in the in-plane direction) to decrease it. FIG. 11 schematically illustrates the expansion and contraction and the deformation of a piezoelectric element 755 bonded onto a substrate 751. FIG. 11 is a conceptual drawing and does not reflect the actual dimensions.
Since the substrate 751 has some rigidity, it has elastic force. For example, if the piezoelectric element 755 expands as shown in FIG. 11, the piezoelectric element 755 tilts toward the substrate 751 due to the elastic force of the substrate 751. This tilt causes decrease in the expansion and contraction stroke of the piezoelectric element 755 by 40%. In order to increase the expansion and contraction stroke as much as possible within a limited voltage range, this decrease in the stroke due to the tilt becomes a big loss, which should be prevented.